The instant invention relates to bimetallic, disc-actuated, thermostatic switches and the like, and more particularly to a novel construction for such switches particularly suited for miniaturization.
As a result of the growing trend toward the miniaturization and weight reduction of electrical components in today's industry, a substantial need has developed for a reliable bimetallic, disc-actuated, thermostatic switch construction which is readily adaptable to miniaturization. In this connection, while the heretofore known bimetallic, disc-actuated, thermostatic switches have proven to be effective and accurate in most applications, they have not been readily adaptable to miniaturization. This is a result of the fact that substantially all of the bimetallic, disc-actuated, thermostatic switches heretofore known have relied solely on direct unamplified disc flexing movement to move contacts in order to effect switching. While this type of switch construction is effective in applications where switch size is not critical, it is not readily adaptable to miniaturization. Unfortunately, as the size of a bimetallic disc is reduced, the amount of flexing movement or snap travel which is capable of being exerted on a movable contact is correspondingly reduced. Since a certain minimum amount of contact travel is essential to effect accurate switching, the size of the bimetallic disc cannot normally be reduced beyond certain minimum limits. The only exception to this has been where switch components have been produced in accordance with critical tolerancing, which has greatly increased their cost.
The instant invention provides an effective bimetallic, disc-actuated, switch construction wherein the movement of a bimetallic disc is amplified so that adequate contact movement can be achieved even when the bimetallic disc is of relatively small size. In particular, the switch construction of the instant invention includes a base having a fixed contact thereon, a fulcrum which extends upwardly from the base and is spaced from the fixed contact, and a support post which extends upwardly from the base spaced on the opposite side of the fixed contact from the fulcrum. A resiliently deformable actuator disc having a peripheral ring which defines an interior open area, and having an integrally struck actuator arm which extends radially inwardly from the ring into the open area, is secured to the base by the support post with the arm of the disc overlying the fulcrum and extending to a point adjacent the fixed contact. A bimetallic disc is positioned adjacent the actuator disc in the switch and is retained in general alignment. therewith by a housing which also encompasses and protects the components of the switch. When the bimetallic disc flexes in response to a predetermined temperature change, the central portion thereof engages an abutment on the housing so that opposed edge portions of the bimetallic disc are simultaneously pressed against both the support post and the ring of the actuator disc adjacent to the actuator arm. Since the support post is rigid, this causes the actuator disc to be resiliently deformed whereby the actuator arm pivots on the fulcrum to move the terminal portion of the arm either away from or into engagement with the fixed contact. Since the actuator arm has the effect of amplifying the movement of the bimetallic disc as the former pivots on the fulcrum, this permits electrical continuity between a movable contact carried on the actuator arm and the fixed contact to be accurately gauged for opening or closing, even when the bimetallic disc is of miniature size. Movement of the arm is further maximized due to the fact that pressure on the actuator disc is exerted by an edge of the bimetallic disc, where the snap travel of the latter is the greatest. When temperature conditions permit the disc to relax and return to its normal position, pressure on the actuator disc is relieved and the actuator arm resiliently and automatically returns to its original position. The novel concept of amplifying the flexing movement of a bimetallic disc through a lever arm in this manner permits the miniaturization of bimetallic, disc-actuated, thermostatic switches without substantial reductions in the accuracy or effectiveness thereof.
Thermostatic switch constructions representing the closest prior art to the instant invention of which the applicant is aware are illustrated in the U.S. patents to MALONE, No. 2,632,824; MALONE, No. 2,823,283; EPSTEIN, No. 2,864,918; STAHL, No. 3,170,998; MORO, No. 3,329,788; NARDULLI, No. 3,577,111; TAYLOR. No. 4,152,998 and TAYLOR, No. 4,160,226. A number of the above patents illustrate thermostatic switch constructions wherein a radially extending arm is blanked from a bimetallic disc so that when the disc is stressed, the arm will swing upwardly or downwardly to open or close the switch. Examples of switches of this type are disclosed in the patents to TAYLOR and EPSTEIN. The MORO patent teaches a thermostatic switch construction wherein a bimetallic disc imparts movement to a radial arm in a separate circular member to open or close the switch. However, the radial arm does not cooperate with the bimetallic disc in the manner taught by the instant invention. Nor do any of the other patents, including TAYLOR or EPSTEIN, illustrate or teach the combination that characterizes this invention.
For all of the above reasons, it is the primary object of the instant invention to provide a reliable and accurate bimetallic, disc-actuated, thermostatic switch construction which is suitable for miniaturization.
Another object of the instant invention is to provide a means of amplifying the snap travel of a bimetallic disc in a thermostatic switch.
Other objects, features and advantages of the invention shall become apparent as the description thereof proceeds when considered in connection with the accompanying illustrative drawings.